Water-heater



E. S. STACK.

WATER HEATER.

APPLlcAnoN H LED mma. |914.

Pat \11ted.lu11e 10, 1919.

3 SHEETS-SHEET I.

E. S'. STACK.

WATER HEATER.

APPLgcATloN FILED 1AN.23.1914.

Patented June 10, 1919.

3 SHEETS-SHEET '2.

Wauw. A

me Nafems Hens co.4 nuora-www msumcmu. n c.

E. S. STACK.

WATER HEATER.

APPLICATION FILED mm3. 1914.

Patented June 10, 1919.

' sns Parnu one.

ELMER S. STACK, OF WESTSOMERVILLE, MASSACHUSETTS.

wernannnrnn.

Specification of Letters Patent. Patented June 1G, 1919.

` pplicaton led January 23. 1914. Serial No. 813.905.

To all whom z'z may concern.'

Be it known that I, ELMER STACK, a. citizen of the United States, and resident of West Somerville, in the county of Middlesex and State of `Massachusetts, have invented certain `new and useful Improvements in Water-Heaters, of which the following is a specification.V

The present invention relates to a heater 'to cause a continuous circulation ofthe fluid to be heated whether any of the fluid is being drawn off or not, and the location of a thermostatic heat-controlling device in a part of the heater which is shielded to some extent from the direct heat of the heating agent, but in such a Way that the hea,tcontrolling device is exposed to the incoming fluid and to the circulating fluid when there is no withdrawal from the heater.

The importance of the rst of these features becomes apparent when it is realized that in water heaters, Vand particularly those which are heated by the flame from a gas burner, a great deal of trouble has been experienced by condensation of water from; the products of combustion on the parts of the heater which are exposed to the iame. In all the heaters of this character heretofore produced, so far as I am aware, the water or other fluid to be heated is caused to How from the main directly into .a coil or into tubes which are exposed directly to the products of combustion rising from the burner. These products contain a considerable proportion of water v apor, part of which is produced by combustion of the fuel and part of Awhich is present in the air furnished -to support combustion. The water which enters such coils or tubes is frequently, and usually, at a low enough temperature to cause condensation of this water vapor, which gathers on the tubes and drips upon the burner, checking theV flame and causing rapid deterioration ofthe burner higher than that which causes of the water vapor in the products of com- "itself by corroding the metal of which it is composed. My invention avoids this effect by first bringing the cold incoming fluid into thermal contact with the already heated Huid in the heater, before allowing it to pass into those tubes which are directly exposed to the flame, and maintaining such thermal contact for a period long enough to heat the incoming fluid to a vtemperature condensation bustion.

The other feature of the invention secures improved results in maintaining an even temperature in the Huid in the heater, in

enabling the heater to respond quickly to demands for the heated fluid, and in effectlng a marked saving in the use of fuel or vother heating agent, enabling such heating agent to be used with the greatest efficiency and Without waste.

A heater containing my inventions may be used in any situation where the necessity for supplying heated fluids exists. It is particularly adapted to those situations where instantaneous hot Water is demanded Vand the demand for the same is relatively infrequent, so that it would not be the best economy to employ a supply tank in connection with the heater. It is to be understood, however,` that in thus specifying a particular situation forwhich the present improved heater is particularly adapted, I do not thereby intend in any way to ind`1 cate a limitation in the use of the heater or in the scope of the invention, since the principles of my invention are applicable to all places and conditions in which a heater for fluid may be necessary or useful. As heaters of the type to which my invention is here shown as being applied are mainly used for heating Water, I shall in the following description refer to the fluid Fig. 2 is a vertical central section of the heater shown 'in Fig. 1.

Fig. 3 is a modified form of heater embodying the essential principles illustrated in Fig. 2.

Fig. 4 is an elevation of a coil adapted to forin part of the heater and embodying another form of means from that illustrated in Figs. 2 and 3 for producing thermal contact between the incoming water and the heated water.

Fig. 5 is a sbctional view on a larger scale of a part of the coil shown in Fig. 4.

Fig. 6 is a sectional view illustrating the principles of the invention applied to a series of heating units.

The saine reference characters indicate the same parts in all the figures. l

Referring first to Figs. 1 and 2, 1 represents the water tubes through which theV water iows while being heated and 2 represents a gas burner for generating the heat for heating the water. The tubesl pass between upper aiid lower headers 3 and 4, respectively, which are preferably shaped somewhat as hollow coiies. The construction and arrangement of headers and water tubes is preferably substantially that shown in my Letters Patent 0f the United States for water heater, numbered 1,125,753, and granted January 19, 1915, the tubes 1 being set into the conical faces of the headers and firmly securedtherein, and extending from one header to the other in nearly vertical lines, but somewhat offset laterally and angularly about the axis of the heater in order more eectively to intercept the ascending currents of hot gases from the burner. The headers are connected together centrally within the cluster of tubes 1 by a central tube or conduit 5 which is sufficiently large to permit of free flow of water and to contain a therniostatic element as will be presently explained.

1n the preferred construction the cold water inlet and the hot water outlet are formed in a single connection 6 which has a coupling portion 7 attached to the upper header, an inlet coupling S with which the cold water supply pipe 9 is connected, and an outlet coupling 10 with which the hot water delivery pipe 11 is connected. An inner elbow-like conduit 12 is formed in the 'connection in communication with the inlet 8 and is turned toward the header 3, being furnished with an extension 13 which eX- tends well into the header and preferably into the central connecting tube 5. The conduit 12 and its extension 13 are of such di- Inensions and so located that a suiiiciently wide space is provided around them in the connection 6 to permit free outiiow of the heated water without material impedance.

The conduit 14 for supplying gas tothe burner passes across the heater below the lower header and is connected with or contains a valve casing 15 which is crossed by a partition 16 having an aperture surrounded by a valve seat. A valve 17 coperates with said valve seat and is normally held seated by a spring 18 which, bears against the valve and abuts on a cap 19 which closes the cavity 'or branch of the valve casing in which the valve and spring are contained. A frame 15a is connected with the valve casing and supports the niechaiiism whereby the thermostat operates the valve with an accelerating motion. frame is connected by a Vtube 20 with the lower header. 1n they tube is screwed a plug 21 wherewith is connected a thermostaticV tubular element, or tube 22 smaller than the tube 2O and located within the latter, Amade of copper or .any other suitable material which hasa sufliciently great'coeflicientof expansion. This thermostatic tubey passes through the lower header and'into the tube 5 toward the .water vthe free end of the element may Vocciir with changes in the temperature of the water,

This

inlet condiiit`13'. .Pref- K. ei'ably the thermostatic element `extends and is also arranged so that it is thermally `acted upon directly by the incoming water.

The end of the therinostatic element is closed, and acts upon the end of a rod 23, which may be of carbon, steel, or of any otheil suficieiitly hard material having a suiiciently low coelfieient of expansion. The rod 23 bears on a lever 24 pivoted at 25,and

Vacting through an lantifriction roll V2,6 on a Vlever 27pivoted at 28. The lever 27 carries a stem 29 which bears on the stein 30 of the valve. Stem 29 is adjustablebeing screwed -into an internally threaded socket in the arm 27, which socket is divided and its branches are clamped against the stein 29 by a clampV screw 31, to maintain the adjustments.L As will be readily understoodthe adjustments of the stem 29 determine the temperature which is given to the .water in the heater, by Vhastening or retarding the opening of the valve. Y -l A pipe 32 leads from the valve 15 and is conducted in any manner suitable to the flaring admission end of a draft, tube-33 which conducts mingled gas and air to the burner 2. A pilot burner 34V is connected to the gas conduit 14 on the supply side of the control valve 17.

The operation will be readily apparent from an inspection of the drawings in connection with the foregoing description. The

cold water which enters the heater when hot water is drawn therefrom, issues directly Aagainst the thermostatic element and flows through the relatively narrow .space sur-A4 rounding the tliermostatic element in the tube 5 before it enters the heating tubes 1.

` 5 into the lower header 4 45 valve to become i c5 ymay be shut off by a cock In this way the thermostatic tube is exposed throughout its whole length to water at substantially the temperature of the supply. The. consequent contraction of the thermo- 5 static element causes the valvey 17 to be .opened widely and to produce a hot flame at the burner. The course of the water after issuing fromthe extension 13 of the inlet conduit is downward through the tube and thence up- Award through the heating tubes 1 to the `upper header 3. In passing through the tubes 1 the water is sub-divided into small Volumes and is rapidly4 heated, being deliv- 15,ered to the upper header at the desired temperature. Thenceit flows 'through the connection 6 in the annular space surrounding the inlet conduit 12 and extension 13 and so to the delivery pipe.

When the demand upon the heater is equal to the fuel supply .capacity ofthe heater Athe water circulation is that described, and thethermostatic element is exposed to the lowest temperature possibleand the flame at the burner is turned up tothe maximum extent. When the demand for hot water is reduced, the hot water is not able to pass out from the connection as rapidly as it enters the header '3 from the tubes 1;V and when there is no demand for hot water at all there 1s no escape for the heated water. In each case a gravity thermal circulation is set up, inthe course of which the water exposed to heat in the Vtubes 1 rises, and enters the header-3, while the coolerwater in the header 3 andv tube 5 naturally flows downwardly through the tube 5 to the header 4 .and thence to the tubes 1. This circulation continues when any flame is produced at the main burner 2 or at the pilot burner 34, and Y has the eect of heating the water in the tube 5 and expanding the thermostatic element 22, relieving the pressure which tends to open the gas valve 17 and allowing such partly or wholly closed, according to the temperature. 4 In this apparatus the pilot flame produced at the burner 34 has a function additional to that of ignitingtheflame at the main burner when the valve 17 is opened.`` This addiy tional function is to supply heat to the heater sufficient to maintain the thermal cir-.

culation described and to maintain the temperature of the heater at that degree at which the thermostat keeps the valve closed.

If the heat of the pilot flame should not be sufficient for this purpose and the water in the heater cools off, the thermostat contracts and opens the main burner valve, furnishing ,more heat until the predetermined temperatureis again given to the water. When the heater isV to be out Aof service for a considerable period of time, the gas supply to both the main burner and the pilotmburner 35 in thefgas main. i

It will be noted that the thermostat is contained in a part ofthe heater which is not directly exposed to the heat of the iame, but is shielded to a considerable extent from the iiame by the outer enveloping tubes 1. These tubes being preferably arranged in three or more enveloping series, as in my patent hereinbefore referred to, intercept and absorb a great proportion of the heat delivered by the l i part 5 of the heater could be made of greatly Iincreased diameter,

and the diameter of this part could be further increased by somewhat altering the positions of the tubes 1 without departing from the principle of the invention. Further the thermostat is so located, as above described, thatl it is surrounded by the coldest water in the heater, namely the entering water, so that the thermostat is heated and caused to act not by the direct heat of the burner or heating agent, but by the circulation of water induced by thermal action.

It will be noted that the inlet for the cold water passes through thewater in the header 3. Thereby the incoming water is brought into thermal contact with the hottest water in the heater. If desired an obstruction or baffles may be placed in the tube 13 to retard the flow of water through the same and thereby prolong the thermal contact. Fig. 2 shows a helical baflie 36 which provides a winding passage Within the tube 13. This obstruction may be of any length, or it may be entirely omitted, and the tube may be shortened so as to permitan actual mingling of the cold water with the heated water before passing into the central tube 5. In any event the heater is so designed that the cold water becomes somewhat heated before entering the tubes 1, which tubes are the portions of the heater exposed to the products of combustion rising from the burner, so that when the water enters these tubes it will be at a higher temperature than that which would cause condensation of the water vapor in the products of combustion. By this means the highly objectionable e'ect which is so common in gas water heaters, namely that of condensation of water on the tubes or coils, is avoided.

While the heater as above described and herein illustrated is the one which at present I consider preferable, yet I do not limit y.the invention here claimed to the details here out depart-ing from my invention. .isit an essential feature of the invention that the thermostat should be fixed in the bottom of the heater and project upwardly. It is `eolually within the contemplation of my invention to mount the thermostat in the top of the heater, and it may be so mounted `consists of tubes without departing from the spirit of the invention provided it is exposed to the water in that part of the heater where the temperature changes of the water are the greatest and most rapid.

It will be apparent that the regulation of the supply of gas to the heater is in proportion to the demands upon the heater, since the temperature in the tube 5 varies according to the rate at which the hot water is drawn off and the cold water enters, and the thermostatic element in such tube is correspondingly elongated or contracted. It is evidently possible therefore by suitable regulation to enable the heater to deliver water at a certain definite temperature in any quantities up toits maximum capacity, and also to alter the temperature at which the water is soA delivered.

VFig. 3` illustrates a modification of the heater shown in Fig. 2, in which` the ther- Inostat `is contained in a tube 51 external to the heater proper. As before, the heater 1, headers 3 and l and a central tube or-column 5. The latter, however, need not' be a conduit for water, but may be so made as only to perform the function of holding the headers and tubes 1 in proper retationy to one another. The inf coming cold water enters through a tube 91 contained in and passing through the header, such tube being preferably formed into a coil within the header so as to prolong the thermal cont-act betweenthe tube and the hot water in the header. The discharge end of tube 91 passes into a pipe orthimble 92 connecting the tube 51 with the upper header. The lower end of tube 51 is connected with the lower header by a lateral tube 92 and an upright tube 93; The burner" 2 is indicated by dotted lines. In this embodiment the thermostat and the position of the controlling valve are reversed from the arrangement shown in Fig. 2. The controlling valve casing 151 is fixed to the upper end of tube 51, and the latter tube contains a plug 211 to which the thermostatic Y element or tube 220. is secured. The lower end of this thermostatic element is the movable end and is the one which is closed` and which acts upon the less expansible rod 230.

This rod is shown as directly connected to i ame,

the gas controllingvalve 171, but obviously Vsubstantially the same manner as illustrated in Fig. f 2.V Otherwise the gas controlling valve and the connection from the same to the burner are substantially Ythe saine as illustrated in Figs. 1 and 2. It is to be noted that aspa'ce is providedbetween the end of tube 91 and the walls vof the connection 92. Thisspace provides for a free thermal circulation of water when no wateiisbeing either withdrawn from oradmitted to the heater. Such circulation is produced by thel heated water rising in the tubes f1 and by the cooler" water in the ing. This embodiment of the invention also contains the described features of mylinvention, comprisino' a means for'heatingthe incoming Water 2before `adrniti'fin'gw it to the tubes which arewdirectly exposed Vto the and therefore avoiding .condensation uponv such tubes; anda thermostatic control device which is exposed first toithe incoming water, and past which there is a continuous circulation of water whether hot water is being drawn'from the heater or not. In this case also the thermostat is not in the part of the heater which is exposed to the direct heat of theburner, but is "outside of tube 51 descendsuch part. V'Although I have not shown thel externa-l casing ofthe heater in Fig. 3, it is part of my contemplationv either to'mount the tube 51 entirely outside of the casing, or if desired, to interpose a shield between the iiame vfrom vthe burner and the tubev 51, in that case keeping the tube within the main casing. i A

Figs. 1' and 5 illustrate the application of that feature of the invention which relatesto preheating the entering water, in a heater of the coil type.v I-Iere a coil 37 of any ordinary or other preferredcharacter is. provided and is intended to be contained in a casing over a burner, designated 2 andindicated by dotted lines in Fig. 4.' The lower portion 38 of this coil is compound, consisting of an inner tube or conduitV 39 and a j acket'` 40. The cold water flows through the inner tube `39, to the lower end ofwhich it is delivered by thev admission pipe 95, passingfrom the'jacket to the upperV end of thecoil 37 through a conductor 41 which is joined with the Vupper end of the jacket 40 at '42. Then ythe flow through the coil continues from the top to the bottom, the water coming intonthermal end of the jacket 40. The coldwater entering the coil passes first through the pipe within the jacket, which is immediately oyer the burner and contains the hottest water Vin the coil; Thereby the incoming` water is iso volves out to thedeliveryzpipe. It will be evident' that the arrangement last described embodies the feature ofmy invention which inpreheating the entering water by the already hot water in the heater before the incoming water is admitted to of the heater which-is directly exposed to the products of combustion of the heating agent rising from the burner. i

Aheater having the characteristics hereinbefore described lends itself to use in various combinations for quickly heating large and greatly varying amounts of water with a lit- .tle expenditure of gas. Y For instance, a number of such heaters may Abe coupled in series,

the main being ydelivp ered to the viirst of the series, the hot waterV the cold water from discharged from this heater being connected to the inlet of the next heater, and so on, un-` til-.the outlet of the last heater is coupled toA the delivery pipe. `Such an arrangement, embodyinga thermostatic control for each heater and provisions for preheating the inthrough the hot water conduit 110 coming water is illustrated in Fig. 6. This heater, or heating-series, contains three heating elements 100, 101, and 102, eachbeing preferably, although not necessarily,` a duplicate of the heater shown in Fig. 2. `Each heater has its own burner, fuel supply valve, and thermostatic regulator, which may be identical with the .corresponding elements shown in Fig. 2, or with those 'shown in Fig. 3, or may be otherwise made or modiiied without departing from the spirit of the invention. Thermostatic elements for the `various heaters are indicated 223. The water to be heated is delivered by af pipe 96 which `passes into the rstV heater 100 in the manner illustratedin Fig. 2. The circulation in this heater is as already described in connection with Fig.` 2, and the hot water passes through a connection which has a branch 6l coupled to a pipe 62 leading toga coupling 63, which maybeof the saine character `asthe coupling 6 shown in Fig. 2,. A branch 132 leads into the second-heater in which the water circulationV takes place as before, and from which the water now further heated passes throughthe outleti64 ofcoupling 63 to a similar coupling 65 connected witha `third heater. ,4 The outlet of the last coupling is joined to a pipe 110 having a nipple 111 with which the delivery pipe is connected. The inlet pipe 96passes and is given a preliminarydegree of heating by the hot water therein, being raised as in the embodiments of the inventionV previously described, to a degree at which it will vbe ytoo that portion` at 221, 222, and

warm to condense the water vapor in the products of combustion generated from the burnerof the first heater. A baljie or obstruction 360may be provided Vin the inlet pipe 96 to prolong the thermal contact, and such obstruction may be of any length or may be omitted entirely as circumstances warrant. A

Aheater of the sort last described contains" all the principles and advantages hereinbefore discussed, besides having the additional advantage of meeting widely varying demands and furnishing greatly varying quantities of hot water at the desired temperature and without waste of the heatingagent. The individual heaters of this combination are4 designed to permit the maximum rate of flow required of the conditions in which the apparatus is installed, while the burner or heating element of each heater is insufiicient to-heat the water to the required temperature, when the duty is at the maximum, in any one heater. Under this condition the coperation of all of the heaters jis required to bring the water deliveredto the desired temperature, and a portion onlyof the heatrequired is absorbed by the water in each heater.` The individualthermostatic controls of the various heaters automatically control the amount of heat given by each heater to the water, causing the burner of one or more heaters to be wholly or partially opened according. as the demand Vfor heat is greater or less than can be furnished by one heater. Where thedemand is very light, one heater running at full or reduced capacity suflices to heatthe water to ,the required temperature., and although the water after being thus heated in the first heater passes through the other heaters in succession, its temperaure is so high as to cause the thermostatic. controls of the other heaters to sluit down the flame at the burners of those heaters. Likewise when the demand for heat is greater than one heater can supply but not `quantity heated to too high a temperature.

The apparatus now under consideration is infactan instantaneous hot water heater capable of furnishing hot water in any' quantity or at any rate of flow up to a predetermined maximum, at a predetermined and regulable temperature without varia- Contact with said tu es.

tion in temperature, and without wasteful consumption of f gas when the demand is light. Under all conditions the fuel Vis used with the maximum efiiciency so as to get the maximum heating effect. .At all times the heat developed is regulated by the temperature of the water so that the heat generation is exactly proportioned to the demand, and more or less heat is furnished by turning on or shutting off the gas according as the temperature of thel water in the heaters varies, the changes in the heat supply being practically simultaneous with changes in the water temperature. Y

vAL feature common to all of the forms of the invention in which the hereinbefore described water circulation is possible, is that the pilot flame maintains a moderate heat in the water even when none is being drawn from the heater. The circulation distributes the heat throughout the entire body of water in the heater. This is a factor which conduces greatly to the rapid delivery of hot water when required, inasmuch as the relatively high temperature at which the water isl always maintained enables .the water to be brought to the desired higher temperature more rapidly than would `be.

possible if'this continuous circulation under the heat of the pilot liame did not take place.

It ,will be apparent fromr the foregoing descriptionl that all embodiments of the in`- vention here illustrated have this feature in common, that they provide means by which the cold water entering the heater isrst brought into contact with the highly heated water, and is thereby raised in temperature to such Adegree that when entering the tubes moredirectly exposed to the heating agent, it is too warm to cause condensation of water vapor in the aroducts which pass in Thus in the form shown in Fig. 2 the tube 13, in that of Fig. 3 the tube 91, in that of Fig. 5 the tube 39, and in that ofFig. 6 the tubes 96, 132, and the equivalent of 132 in the heater 102, are interior tubes which are shielded by an outer wall or jacket and the body of hot water contained -in said outer member, from the products of. combustion. The outer member, wall, or jacket of Figs. l and 5 is the jacket tube 4:0, of Fig. 3 is the header 3,and in Figs. 2 and 6 is in part the header 3 and in part the central tube 5 of the headers shown therein. And in each case that part of the heater structure whether it be called a jacket, header or what not, into which the entering water is first admitted, is that which contains the hottest water in the entire heater. Being conducted through such jacket, header, or member in a manner whereby it is shielded from the productsl of Y combustion, the entering water cannot chill such products of combustion and such water before it can arrive in contact with the sur-4-V faces'which are directly exposed to the prod, ucts of combustion, isA warmed beyond the point at which it would causecondensation.V For the purposes of this description' ,theterm inner tubemay be considered as including the tube 13, tube 91', tube39,tube 96, and tube 132, or any essential equivalent` of such tubes; and the term outer member j as including any sort of a V-jacket-orpart 75 such as the jacket 40 or header 3, or equiva- Y lent member correspondingly arranged -to inclose the inner tube and hold` a body of liquid so as to surround `the inner tube.

I desireto state that-inspeaking of the heating element of Vthejheater as algas burner and of the heatingV agent as gas, I have not intended to limit inventionto ani apparatus in which heat is generated" by thev combustion of gaseous fuel, neither have 178 intended t0 limit the invention to'an'ap-V paratus in whichheat is developed by the combustion of any fuel;V In respect to thev heat regulator I- reserve the right to employ any` suitable heater which is 4suloj ect to control and regulation, whether such heater lis la burner for gaseous fuel, av conductor for a previouslyrheated iiuid" (as steam), the flowl of which iscontrolled by afvalve,vare1of any sort controlled byl dampers, valves, or screens, orheat generated electrically, under government of any sort of controller capable of being operated by a thermostat. i j 'i What I claim and desireto secure by Letters Patent is: Y A V f 1 1. A ,water heater fordomestic use Vcomprising an inlet, an outlet, ia conducting tube into which said inletdischarges and from which the ywater is displaced by the water'- entering theinlet when escape from the out# 105 let is permitted, a burner arranged to direct 'the products of combustion of gas againstV said tube, and an'external container between said'tubeand 'the outlet, into whichV the tube discharges and in which the inlet V is contained. c Y

2. A heating apparatus'comprising a heating unit having an inlet, a 'circulating sys'- tem of tubes and an outlet, a second heating unit having an inlet connected with the outlet of the first heatingunit, vhaving a circulating system of tubes andf4 having anoutlet, `a receiver to which said outlet is connected and to which thelheated iiuid is delivered and a conductor 'passing through 1-20 said receiver and connecting withthe inlet of the first heatingunit, being so arranged to preheat the incoming liquid before the delivery thereof to thel tubesl of the rst Y heater. j y 125 3. A. heater including in its construction Y heating tubes exposed to a heating ame, upperand lowerheaders to which said tubes are connected, a circulating tube extending Y from the upper tothe lower header, and 13'0 means for leading the water to be heated culating tube, whereby the water is warmed before entering the heating tubes, to avoid condensation on the external surface of said heatingtubes, of the water vapor contained in the products of combustion of the heating flame. v f

4. A non-condensing heater comprising upper and lower headers, a collection of heating tubes extending between said head-V ers and communicating therewith, a burner arranged to direct products of combustion of burning gas upon said heating tubes, a circulating tube leading from the upper to the lower header and a cold water inlet arranged to direct the incoming water through the upper header into the circulating tube and thence to the lower header and the heating tubes, whereby the Water is preheated before entering the heating tube to a temperature above that which causes condensation Copies of this patent may be obtained for ve cents each, by addressing the of the water vapor in the products of combustion.

5. A water heater comprising circulating means through which water is caused to ow in thermal Contact with heated products of combustion, a chamber or outer member into which hot water is delivered by said circulating means, and an inlet for water to be heated arranged to cause such water to pass through the interior of said outer member in its course to the circulating means, whereby the incoming water is heated by thermal contact with already heated water in the heater, and before its admission to said circulating means, to a temperature above that at which it would cause condensation of water vapor in the products of combustion. In testimony whereof I have'aiiixed my signature in presence'of two witnesses.

ELMER S. STACK. Witnesses:

ARTHUR H. BROWN, P. W. PEZZETTI.

Commissioner of Patents,

Washington, D. G. 

